1. Field of the Invention
The present invention is directed to a medical electrode device implantable in a subject for stimulating tissue, and in particular to such a device which incorporates means for explanting the device.
2. Description of the Prior Art
Medical electrode devices are well-known in the art for the intracorporeal stimulation of tissue. Such electrode devices include an electrode cable containing an elongated, flexible conductor with an exterior covered by an insulation layer, and an interior forming a channel. The distal end (i.e., the end of the electrode device disposed at the stimulation site) is provided with an electrode head, electrically connected to the conductor. A stylet is insertable into the channel from the distal end (i.e., the end to be connected to a pulse generator) of the electrode device, the stylet normally being used to assist in the implantation of the electrode device, but also being usable, if necessary, to assist in the explantation of the electrode device, should such explantation become necessary.
Such an electrode device which is permanently implanted in a patient, such as a pacemaker electrode, becomes coated over time with connective tissue which anchors the electrode cable in such a way that pulling only on the exposed proximal end of the electrode cable, in order to explant the cable, can be very difficult and even hazardous, because healthy tissue in the area at and around the anchoring site may be torn or otherwise damaged. The physician therefore often elects to leave the electrode cable in place, and to replace it with another cable. Under certain instances, however, removal of the electrode cable is warranted, either by surgery or with aid of an explantation device. Such instances include, for example, the presence of multiple abandoned, disconnected electrode cables in the heart, which can result in the development of infection, or the electrode cables may threaten to puncture a vein or the heart wall.
An explantation device for such an electrode cable is described in the article entitled "Removal of Chronic Implanted Leads Using a New Technology in 25 Cases" Hocherl et al., European Journal of Cardiac Pacing and Electrophysiology, Volume 2, No. 2, June 1992, page A77. In this explantation device, the distal end of a stylet-like member has rearwardly facing projections which substantially flatten against the stylet-like member when the member is introduced into the channel of the electrode cable. The projections subsequently snap outwardly and press against the inner wall of the channel. During explantation, the physician pulls on the member, and the projections then grip the flights of the helically-wound conductor which form the inner wall of the channel. A disadvantage of this known explantation device is that only the small, free end surfaces of the projections engage the interior wall of the channel, and may deform and stretch the helical shape of the conductor to such an extent that the projections lose their grip, at least in part. Another disadvantage of this known device is that the explantation device cannot be repositioned or withdrawn from the channel, because of the projections.